1. Field of the Invention
This invention relates to a digital indication type dimension measuring instrument, and more particularly to improvements in a shock absorbing mechanism provided for stabilizing a displacement speed of a spindle and controlling an overspeed.
2. Description of the Prior Art
There has heretofore been known a digital indication type dimension measuring instrument in which a displacement value of a spindle is detected by a displacement detection portion, such as a photoelectric encoder and a magnetic encoder, and a dimension, a position and the like of a workpiece to be measured are digitally indicated. In the digital indication type dimension measuring instrument of the type described, even if an encoder of any type would be used as the displacement detection portion, there should be a limit in detectable speed due to circuitry economics or other. For this reason, it becomes necessary to provide a shock absorbing mechanism for preventing the overspeed of the spindle. Furthermore, in order to prevent a measuring element at the forward end of the spindle from crashing into the workpiece so as to provide a safe and high precision measuring, and further to stabilize or uniformalize a displacement speed of the spindle, it is necessary to provide the shock absorbing mechanism. As the shock absorbing mechanism as described above, mention may be made to a dashpot type shock absorbing mechanism which acts against a resilient biasing force when the spindle is resiliently biased in a predetermined direction. When a dashpot type shock absorbing mechanism is used, it is particularly advantageous in stabilizing a displacement speed of the spindle.
However, the conventional dashpot type shock absorbing mechanism has been designed on the basis of the case where the spindle is held in an erected state and dropped vertically. In consequence, when the spindle is levelled or tilted in the use, the gravity effect on the spindle disappears or is reduced, whereby the shock absorbing mechanism excessively acts as compared with the resilient biasing force, thus resulting in an excessively slow displacement speed of the spindle.
For the above-described reason, a period of time, for which the measuring element provided on the spindle comes into contact with the workpiece, becomes long. As a result, the accumulation in resultant lost time, is considerable from the viewpoint of the measuring tasks of today, particularly in mass production systems. Although the digital indication type dimension measuring instrument provides an instantaneously readable, numerally indicated measured value differing from an analogue indication type dimension measuring instrument, the instant readability cannot be satisfactorily displayed if the displacement speed of the spindle is slowed to an unnecessary extent. Further, the speed of response tends to be decreased while the workpiece is moving.